Though infection is an uncommon complication of arthroplasty, it may have devastating complications, both physical and economic, for a patient and for the healthcare system. Infection following total knee arthroplasty can be difficult to diagnose, and is often difficult to treat once it has been diagnosed. The revision procedure that must be undertaken once an infection has been identified typically involves a combination of surgical debridement to decrease the bacterial bioload as well as revision of one or more components of the prosthesis, and prolonged IV and/or oral antibiotics to eliminate the remaining bacteria. This will mean, for the patient, a longer operating time, greater blood loss, and more chance for other complications to arise, along with increases in the total number of hospitalizations of the patient, their duration of hospitalization, their total number of operations, their total hospital costs, and the total outpatient visits and charges that they must endure.
Currently, several options exist for the treatment of an infected total knee arthroplasty. The first option is simple suppression of the infection with intravenous (IV) and/or oral antibiotics. This option is generally reserved for patients that are thought for any number of reasons to be unfit for surgery. As a general rule, simple IV and/or oral antibiotic treatment of an infected total knee arthroplasty without concomitant surgery is unlikely to result in eradication of an infection, but may suppress the infection such that it is minimally symptomatic.
The second option is a so-called “irrigation and debridement and polyethylene exchange.” In this procedure, an open irrigation and debridement of the infected knee is undertaken, with concomitant removal of the polyethylene spacer and placement of a new polyethylene spacer (a “polyethylene exchange”). In some instances, surgeons may elect to add dissolvable antibiotic beads to the knee at the time of surgery. Following this procedure, patients are generally placed on at least 6 weeks of IV antibiotics and may then be put on oral antibiotics for an indefinite period of time. The major advantage to this procedure is that it preserves the current metallic prosthesis, thus minimizing the morbidity of removing a well-fixed prosthesis. Removing a well-fixed prosthesis generally results in loss of variable amounts of native bone stock about the femur and tibia, which is of obvious detriment to the patient. The major disadvantage is that it may be difficult to eradicate the infection using this technique. The success rate for eradication of infection varies a great deal, from 31% to 75%. See, for example, S. M. Odum, T. K. Fehring, & A. V. Lombardi, et al., “Irrigation and debridement for periprosthetic infections: does the organism matter?” 26 J. Arthroplasty 6(suppl):114-118 (2011). See also, for example, I. Byren, P. Bejon, & B. L. Atkins, et al., “One hundred and twelve infected arthroplasties treated with ‘DAIR’ (debridement, antibiotics and implant retention): antibiotic duration and outcome,” 63 J. Antimicrob. Chemother. 1264-1271 (2009).
The third option is a so-called “two-stage exchange.” A two-stage exchange consists of two operations. In the first operation, the existing prosthesis and surrounding cement are both removed, a thorough irrigation and debridement is performed, and an antibiotic-eluting polymethylmethacrylate (PMMA) (“bone cement”) temporary spacer is placed in place of the prosthesis. Multiple options for a replacement temporary spacer may exist for this procedure. For example, the temporary spacer may be a static spacer, which consists of a block of PMMA that spans the tibiofemoral space and as such holds the knee in a fixed extended position. The temporary spacer may also be of the articulating variety; in this case, the femoral, tibial, and polyethylene parts of the knee are replaced with antibiotic-impregnated molded PMMA components, which may function as a temporary prosthesis, and which may temporarily elute a high, but ever diminishing concentration of antibiotics into the knee. This articulating device allows for some movement of the knee joint. There are several commercially available varieties of PMMA articulating spacers, some of which come pre-formed and pre-loaded with antibiotics (For example, InterSpace Knee, Exactech, Gainesville, Fla.) and some of which are molded by the surgeon in the operating room (For example, Stage One, Zimmer Biomet, Warsaw, Ind.). Additionally, each of these devices aim to temporarily replace the infected prosthesis. That is, the metal femoral and tibial components are removed and replaced with a temporary femoral and tibial drug delivery implant. Following the first stage, in which the existing prosthesis is replaced with a temporary prosthesis, the patient is placed on at least 6 weeks of IV antibiotics. When the infection is thought to be eradicated, the second stage of the procedure is performed. In this stage, the PMMA spacer is removed, and replaced with a revision prosthesis. The advantage of a two-stage procedure is that it has a relatively high success rate, ranging from 72% to 93%. See, for example, S. M. Mortazavi, D. Vegari, A. Ho, B. Zmistowski, & J. Parvizi, “Two-stage exchange arthroplasty for infected total knee arthroplasty: predictors of failure,” 469 Clin. Orthop. Relat. Res. 11:3049-54 (November 2011). See also F. S. Haddad, M. Sukeik, & S. Alazzawi, “Is single-stage revision according to a strict protocol effective in treatment of chronic knee arthroplasty infections?” 473 Clin. Orthop. Relat. Res. 1:8-14 (January 2015). The disadvantages are the morbidity of two major operations, potential bone loss caused by removal and reimplanation of the prosthesis, a difficult period for the patient when the antibiotic spacer having restricted functionality is in place, and the high cost of revision implants.
A fourth option is a so-called “one-stage” or “single-stage” exchange. In one-stage exchange arthroplasty, the infected metal prosthesis is removed, the joint is thoroughly irrigated and debrided, and a new revision prosthesis is put in place (often with antibiotic cement for fixation) all in one operation. This is uncommon in the United States for fear of failure. If this approach is undertaken, generally a large amount of tissue and bone are resected, which is a clear disadvantage.